The invention concerns the treatment of phosphuretted slag obtained by refining a metallic bath.
It is known that the refining operation for melted metal, such as steel, consists notably in the elimination from the metallic bath of a determined quantity of dissolved elements such as phosphorus, sulfur, among others. One succeeds customarily by forming on the bath a slag for which the essential role is precisely to grow rich in these elements. It is likewise known that certain slag can be formed in this manner, if appropriate measures are not engaged in at the right time, which contain contaminating agents that are sometimes very harmful to man.
This is particularly the case with phosphuretted slag obtained by dephosphorylation of a metallic bath in reducing phase by means of the alkaline earths, such as calcium (see e.g. French Pat. No. 2,428,672-IRSID) or by which is compounded halogenated (see e.g. French Pat. No. 2,356,732-Nippon Steel).
It has been found, in effect, that such slag, rich in phosphorus, cold hydrolyzes upon simple contact with air to produce phosphines according to the reaction ##STR1## where M represents the alkaline earth utilized as dephosphorylating agent.
The phosphine being a very toxic gas, it is indispensable to stabilize the slag before it becomes hydrolyzed.
The known solution (French Pat. No. 2,356,732) involves hot oxidizing of the slag in an atmosphere enriched in oxygen. This is then carried by the phosphorus for formation of a very stable phosphate.
However, the reaction of a gas such as oxygen on a liquid refining slag always presents rather slow kinetics. Moreover, the practicality of the method is notably limited by the necessity of installing particular means in order to assure the blowing onto the slag of a gaseous oxygenated current. Additionally, it is imperative that the slag should be preliminarily isolated from the metallic bath in order to avoid its becoming oxidized or the taking on of phosphorus. In other respects, this is done by cooling the slag for a time. A temperature is then maintained by means of an oxidizing flame burner. However, it is advisable then to utilize a combustible such as gaseous CO in order to avoid that the combustion be accompanied by the formation of water vapor.